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Melanism is considered as a common and highly variable phenomenon in snakes (LORIOUX ET AL., 2008), offering a variety of advantages: faster heating rates, higher mean body temperatures, protection from overheating (LUISELLI, 1992, FORSMAN, 1995, CLUSELLATRULLAS ET AL., 2008, BITTNER ET AL.., 2002, TANAKA, 2005, GIBSON & FALLS, 1979), but also disadvantages, such as higher predation risk (CLUSELLA-TRULLAS ET AL., 2008). In some species, melanism is a Mendelian trait (KING, 2003) and it's appearance varies in frequency due to random genetic drift (BITTNER & KING, 2003). It is not rare among Grass Snake (Natrix natrix) (Linnaeus, 1758) populations, and dark specimens can be found throughout the distribution area (JANDZIK, 2004). The occurence of melanistic colouration among Aesculapian Snakes (Zamenis longissimus) (Laurenti, 1768) is also known, but is far less frequent (EDGAR & BIRD, 2006). In this paper we present several individuals of Natrix natrix and Zamenis longissimus, displaying incomplete melanistic colouration, from various locations in Croatia, found between 2008 and 2010: Diviška (Island of Krk) (two N. natrix, X: 5481675, Y: 4984181), Zmajevac (Baranja) (two N. natrix, X: 5796776, Y: 5080849; one Z. longissimus, X: 5795946, Y: 5080155), Jezero (Island of Krk) (one Z. longissimus, X: 5466553, Y: 5003106), Bizek (Zagreb) (one N. natrix, X: 5566555, Y: 5077558), Majkovi (Dubrovnik) (one N. natrix, X: 5738792, Y: 4740729).
 
Figure 1. Melanistic Grass Snakes from (a,c) Zmajevac, (b) Bizek, (d,g) Diviška, (e,f) Majkovi
 
Figure 2. Melanistic Aesculapian Snakes from (a) Zmajevac, (b) Jezero
 
 
REFERENCES:
BITTNER, T.D., KING, R.B. & KERFIN, J.M. (2002): Effects of body size and melanism on the thermal biology of Garter Snakes (Tamnophis sirtalis). Copeia. 2002: 477-482.
BITTNER, T. D., KING, R. B. (2003): Gene flow and melanism in garter snakes revisited: a comparison of molecular markers and isnad vs. coalescent models. Biologycal journal of the Linnean Society 79: 389-399.
CLUSELLA-TRULLAS, S., TERBLANCHE, J. S., BLACKBURN T. M. & CHOWN, S.L.K (2008): Testing the thermal melanism hypothesis: a macrophysiological approach. Functional ecology 22: 232-238
EDGAR, P. & BIRD, D.R. (2006): Action Plan for the Conservation of the Aesculapian Snake (Zamenis longissimus) in Europe. Convention on the Conservation of European Wildlife and Natural Habitats.
FORSMAN, A. (1995): Heating rates and body temperature variation in melanistic and zigzag Vipera berus: does colour make a difference? Ann. Zool. Fennici 32: 365-374
Melanism is considered as a common and highly variable phenomenon in snakes (LORIOUX ET AL., 2008), offering a variety of advantages: faster heating rates, higher mean body temperatures, protection from overheating (LUISELLI, 1992, FORSMAN, 1995, CLUSELLATRULLAS ET AL., 2008, BITTNER ET AL.., 2002, TANAKA, 2005, GIBSON & FALLS, 1979), but also disadvantages, such as higher predation risk (CLUSELLA-TRULLAS ET AL., 2008).{akeebasubs 6 Month Ratsnake Foundation Membership || Yearly Ratsnake Foundation Membership || Article Access} In some species, melanism is a Mendelian trait (KING, 2003) and it's appearance varies in frequency due to random genetic drift (BITTNER & KING, 2003). It is not rare among Grass Snake (Natrix natrix) (Linnaeus, 1758) populations, and dark specimens can be found throughout the distribution area (JANDZIK, 2004). The occurence of melanistic colouration among Aesculapian Snakes (Zamenis longissimus) (Laurenti, 1768) is also known, but is far less frequent (EDGAR & BIRD, 2006). In this paper we present several individuals of Natrix natrix and Zamenis longissimus, displaying incomplete melanistic colouration, from various locations in Croatia, found between 2008 and 2010: Diviška (Island of Krk) (two N. natrix, X: 5481675, Y: 4984181), Zmajevac (Baranja) (two N. natrix, X: 5796776, Y: 5080849; one Z. longissimus, X: 5795946, Y: 5080155), Jezero (Island of Krk) (one Z. longissimus, X: 5466553, Y: 5003106), Bizek (Zagreb) (one N. natrix, X: 5566555, Y: 5077558), Majkovi (Dubrovnik) (one N. natrix, X: 5738792, Y: 4740729).

Figure 1. Melanistic Grass Snakes from (a,c) Zmajevac, (b) Bizek, (d,g) Diviška, (e,f) Majkovi

Figure 2. Melanistic Aesculapian Snakes from (a) Zmajevac, (b) Jezero


REFERENCES:
BITTNER, T.D., KING, R.B. & KERFIN, J.M. (2002): Effects of body size and melanism on the thermal biology of Garter Snakes (Tamnophis sirtalis). Copeia. 2002: 477-482.
BITTNER, T. D., KING, R. B. (2003): Gene flow and melanism in garter snakes revisited: a comparison of molecular markers and isnad vs. coalescent models. Biologycal journal of the Linnean Society 79: 389-399
.CLUSELLA-TRULLAS, S., TERBLANCHE, J. S., BLACKBURN T. M. & CHOWN, S.L.K (2008): Testing the thermal melanism hypothesis: a macrophysiological approach. Functional ecology 22: 232-238
EDGAR, P. & BIRD, D.R. (2006): Action Plan for the Conservation of the Aesculapian Snake (Zamenis longissimus) in Europe. Convention on the Conservation of European Wildlife and Natural Habitats.
FORSMAN, A. (1995): Heating rates and body temperature variation in melanistic and zigzag Vipera berus: does colour make a difference? Ann. Zool. Fennici 32: 365-374

 HYLA VOL. 2011. No. 2 Str. 39-42  PHOTO NOTE
This site has information on the following genera of Ratsnakes ... Spilotes, Spalerosophis, Ptyas, Zamenis, Elaphe, Rhinechis, Senticolis, Pseudelaphe, Pantherophis, Bogertophis, Orthriophis, Gonyosoma, Oreocryptophis, Oocatochus, Euprepiophis, Coelognathus, Archelaphe